Effect of thermal ageing on tensile and creep properties of JLF-1 and CLAM steels

The thermal ageing treatments of JLF-1 and CLAM steels were performed at 823 K up to 2000 h to simulate in-service condition and at 973 K for 100 h to provide heavy overageing. Hardness, tensile and creep rupture tests were conducted in the aged and un-aged materials. The results showed increase in hardness at room temperature and improvement in creep properties after ageing at 823 K/2000 h for the both steels, implying the strengthening. However, softening and degradation of creep properties occurred after ageing at 973 K/100 h. Lower normalization and tempering temperature of CLAM steel were suggested to be responsible for higher hardness and tensile strength, lower minimum creep rate and longer rupture time, and also for higher susceptibility to the thermal ageing of relatively short term than those of JLF-1.